Kwan committed suicide by jumping into a plasma stream on stardate 47622.1. The motivation for his suicide was initially a mystery to the rest of the crew, as it was not consistent with his personality.

It was later learned that the partially telepathic Kwan had come in contact with a telepathic imprint left since the Enterprise-D was under construction in 2362, by Lieutenant Walter Pierce, who had caught his lover Marla E. Finn with another man, William Hodges, then killed them both, before committing suicide by jumping into the plasma stream. The imprint caused Kwan to experience a hallucination similar to Pierce's final days, in which Kwan believed he had killed someone (most likely Ensign Calloway), compelling him to take his own life in the same manner that Pierce had.

While investigating Kwan's death, Counselor Deanna Troi was affected by the telepathic imprint as well, and nearly suffered the same fate, before being stopped from jumping by Lieutenant Worf. (TNG: "Eye of the Beholder")

An okudagram readout of Kwan's personnel file was displayed on a viewscreen that Deanna Troi was studying. Some of the facts could be called into question since she was involved in a very detailed hallucination when the data was shown. This could explain why he was assigned to three different starships on the same date, and why he was born on a stardate that might indicate he was only seven years old. On the other hand, background graphics are usually inside jokes and other made-up information, so it is probably best not to take them too seriously.